An Evaluation of the Efficacy of Predictive Tests and Anthropometric Measurements in Determining Difficult Intubation in Children

Background: An incidence of difficult intubation in elective surgery is 1.5%–8%. Multiple attempts during tracheal intubation can cause airway injuries bleeding, brain hypoxia, and even cardiac arrest. Unanticipated failure and inability to secure difficult airway can lead to “cannot ventilate, cannot intubate” condition. Preoperative assessment and bedside tests play a vital role in predicting and stratifying risk of difficult intubation. This study was done to determine the incidence of difficult intubation and diagnostic accuracy of different bedside tests for predicting intubation difficulty in patients without airway pathology scheduled for elective surgery under general anesthesia. Materials and Methods: Two hundred patients, aged 20–50 years, American Society of Anaesthesiologists I and II, without airway pathology undergoing elective surgery were evaluated preoperatively using simple bedside tests such as Mallampati grading (MPG), interincisor gap (IIG), thyromental distance (TMD), sternomental distance, upper lip bite test, neck circumference, and atlantooccipital extension to predict difficult intubation. Statistical confirmation was done using Pearson’s chi-square test and univariate and multivariate logistic regression. Results: In our study, the incidence of difficult intubation was observed as 6%. High sensitivity for predicting difficult intubation was seen with IIG > TMD > MPG, and high specificity among the relevant bedside tests was seen with TMD > MPG > IIG. Tests with high positive predictive value were TMD > MPG, whereas high negative predictive value was seen with IIG > TMD >MPG. Conclusion: IIG, TMD, and MPG can be used to predict difficult intubation in patients without airway pathology.

Preoperative bedside screening tests for difficult tracheal intubation may be neither sensitive nor specific enough for clinical use. The aim was to investigate if a combination of the Mallampati classification of the oropharyngeal view with either the thyromental or sternomental distance measurement improved the predictive value. A total of 212 (109 male, 103 female) non-obstetric surgical patients, aged >18 yr, undergoing elective surgical procedures requiring tracheal intubation were assessed preoperatively with respect to the oropharyngeal (modified Mallampati) classification, thyromental and sternomental distances. An experienced anaesthetist, blinded to the preoperative airway assessment, performed laryngoscopy and graded the view according to Cormack and Lehane's classification. Twenty tracheal intubations (9%) were difficult as defined by a Cormack and Lehane Grade 3 or 4, or the requirement for a bougie in patients with Cormack and Lehane Grade 2. Used alone, the Mallampati oropharyngeal view, and thyromental and sternomental distances were associated with poor sensitivity, specificity and positive predictive values. Combining the Mallampati Class III or IV with either a thyromental distance <6.5cm or a sternomental distance <12.5cm decreased the sensitivity (from 40 to 25 and 20%, respectively), but maintained a negative predictive value of 93%. The specificity and positive predictive values increased from 89 and 27% respectively for Mallampati alone to 100%. The findings suggest that the Mallampati classification, in conjunction with measurement of the thyromental and sternomental distances, may be a useful routine screening test for preoperative prediction of difficult tracheal intubation.

Predicting difficult intubation--worthwhile exercise or pointless ritual?

Context:There is an impelling need for accurate tests to predict difficult intubation, as failure to achieve endotracheal intubation causes significant morbidity and mortality in anesthetic practice.Aim:To calculate the validity of the different tests along with their combination and agreement when compared with endotracheal intubation in predicting difficult intubation.Settings and Design:Operation theaters, analytical study.Materials and Methods:Three hundred patients aged between 16 and 60 years of American society of anesthesiologist (ASA) physical status I and II, scheduled for elective surgical procedures requiring endotracheal intubation were studied during January-July 2012. Mallampati grade (MP), sternomental distance (SMD), thyromental distance (TMD), and Delilkan and Calder test were recorded for every patient. Endotracheal intubation was performed by an experienced anesthesiologist blinded to the measurements and recorded grading of intubation. Sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), likelihood ratio (LR), odds ratio (OR), and kappa coefficient of tests individually and in combination were calculated.Statistical Analysis Used:IBM SPSS software (version 16.0) and Epi-info software (version 3.2).Results:Difficult and failed intubation was 13.3% and 0.6%, respectively. Difficult intubation increased with age. TMD and Calder test showed highest sensitivity individually and Dellilkan's test showed least sensitivity. Among the combination of tests, MP with SMD and MP with Calder test had the highest sensitivity.Conclusion:Among individual test TMD and Calder are better predictive tests in terms of sensitivity. Combination of tests increases the chance of prediction of difficult intubation.

Aim: To find out the incidence of difficult airway and which parameter will be suitable to predict it in sikkimese population. Material and methods: This is observational single blinded study was done on 500 patients between 18 to 65 years of age coming for surgery under general anaesthesia . The airway parameters assessed were Modified Mallampati test (MMP), Inter incisor gap (IG), Thyromental distance (TMD), Sternomental distance (SMD) and Mandibular protrusion (MP) along with demographic characteristics. Then difficult intubation was graded according to the Cormack–Lehane classification and was compared with above mentioned parameters. Result: 86 patients had difficult intubation with incidence of 17.20%. Gender and different ethnicity showed significant association. MMP, TMD and among combination test MMP+TMD, MMP+SMD was found to be statistically significant. Maximum AUC of ROC curve was seen in TMD (0.65) followed by MMP+TMD (0.615). The Mandibular protrusion has highest sensitivity (100%). The MMP showed least sensitivity (27.91%) but highest specificity (93%), PPV (45.3%) and diagnostic accuracy (81.8%). The sensitivity for MMP was found to be increased in combined parameters MMP+ SMD (73.26%), MMP + TMD (55.81%). Conclusion: It’s better to use combination of test to predict difficult airway. TMD, MMP+TMD and MMP+SMD can be used.

Various screening tests are done for predicting difficult laryngoscopy with variable diagnostic accuracy. Difficult laryngoscopy is being considered a surrogate indicator of difficult intubation, though it is not the exact measure of intubation difficulty. Our objectives were to find out the better predictor of difficult laryngoscopy amongst the routinely used tests and also to find the ability of difficult laryngoscopy to predict difficult intubation. This prospective, observational study involved 314, ASA I/II adult patients requiring endotracheal intubation. Measurement of sternomental, thyromental and inter-incisor distances and gradings of mandibular protrusion and modified Mallampati were done. Statistical values including sensitivity and specificity of these tests were calculated to find the better predictor of difficult laryngoscopy. Cormack and Lehane laryngoscopy grade III/IV was defined as difficult laryngoscopy. Requirement of >3 attempts for endotracheal intubation was defined as difficult intubation. The sensitivity of the Modified Mallampatti Test for predicting difficult laryngoscopy was highest, 83% compared to other tests. Total 12 (3.8%) patients had difficult laryngoscopy. Intubation was difficult in 7 (2.2%) patients, of which four had difficult laryngoscopy (P<0.001). Modified Mallampati test was better for predicting difficult laryngoscopy compared to other bedside screening tests. Difficult laryngoscop could significantly predict difficult intubation in our patients.

Corresponding author: Kye-Min Kim, M.D., Ph.D., Department of Anesthesia and Pain Medicine, Inje University College of Medicine, Sanggye Paik Hospital, 761-1, Sanggye 7-dong, Nowon-gu, Seoul 139-707, Korea. Tel: 82-2-950-1173, Fax: 82-2-950-1323, E-mail: kyemin@paik.ac.kr Copyright c Korean Society of Anesthesiologists, 2009 cc This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Difficult airway is a major factor threatening the safety of anesthesia. According to the database of the American society of Anesthesiologists Closed Claims Project [1], difficult tracheal intubation is the second most common cause of adverse events bringing about anesthesia-related malpractice claims. To avoid the unanticipated difficult intubation and the catastrophic outcomes, preoperative airway assessment and recognition of difficult intubation are necessary. Several factors such as Mallampati classification, thyromental distance, sternomental distance have been related to difficult intubation [2]. Predictive abilities for difficult intubation of these factors or composite indexes have been tested [2,3]. Postburn sternomental contractures with limited head and neck mobility are considered to increase the incidence of difficult airway. A recent case report on a child with an advanced neck contracture after burn shows us how serious it can be [4]. Therefore, very careful approach to the airway management is required in these patients. In this issue of Korean Journal of Anesthesiology, Jeong et al. [5] compared the predictive abilities for difficult intubation in those patients among three tests: modified Mallampati classification, modified Onah’s classification, El-Ganzouri and Colleagues Multivariate Risk Index (EGRI) [6]. In the study, Jeong et al. introduced Onah’s classification [7] which is originally for guiding surgical options. They modified it by removing elements of surgical consideration and used the simplified form for predicting difficult intubation. In their study, sensitivity and specificity of Mallampati classification for predicting difficult intubation were 97.7% and 19.7%, respectively. On the other hand, sensitivity and specificity of modified Onah’s classification were 86.0% and 84.9%, respectively, which are remarkably improved. Even though the diagnostic performance of EGRI were slightly lower than those of modified Onah’s, they seem to be acceptable also (sensitivity and specificity of EGRI were 83.7% and 75.8%, respectively). On the basis of these results, modified Onah’s classification was more accurate test for difficult intubation than the others in patients with sternomental contractures (Accuracy of modified Onah’s classification, EGRI and modified Mallampati classification were 85.3%, 78.9% and 50.5%, respectively). For safety issue, we must reduce the incidence of unanticipated difficult intubation as far as we can. To do so, we need to use more accurate test for the prediction of difficult intubation in case of postburn sternomental contractures. From this point of view, Jeong et al.’s study has clinical implication. However, we should also keep in mind that there is some probability of false negative prediction even with the most accurate test. So, it is recommended to be careful in the airway management regardless of the results of predictive tests. Furthermore, we should be fully aware of ‘practice Guidelines for Management of the Difficult Airway’ [8] and be familiar with several alternative techniques to laryngoscopic intubation.

IntroductionDifficult intubation is one of the most challenging scenarios to deal with due to increased morbidity and mortality. Machine learning systems can help predict this process in advance. This study aimed to predict whether patients had difficult intubation using machine learning programs for anthropometric and ultrasonographic measurements taken for preoperative airway assessment.MaterialmethodPatients over 18 years of age with American Society of Anesthesiologists (ASA) scores I–III who underwent general anesthesia were included. Patients with a history of head/neck surgery, planned thyroidectomy, congenital or acquired airway anomalies morbidly obese patients with BMI > 40 or a known difficult airway were excluded. Preoperative modified mallampati test score and other anthropometric measurements (thyromental distance, neck circumference, mouth opening, sternomental distance) were recorded. Ultrasonographic measurements included the distance from skin to hyoid bone, skin to epiglottis, skin to vocal cords (anterior commissure), skin to trachea, MTT and hyomental distances in neck extension and neutral positions. The dataset was analyzed via eight different machine learning algorithms.ResultsWe obtained data from 329 patients (62 difficult intubation cases). The Support Vector Machine algorithm achieved the highest performance, with an accuracy of 89.39%, a negative predictive value of 92.7%, and a positive predictive value of 72.7%. Among all evaluated parameters, the modified mallampati score, neck circumference, skin to epiglottic distance and tongue thickness were the strongest predictors of difficult intubation.ConclusionThe ability of individual bedside tests, which are commonly used, to predict difficult intubations is limited. Our study demonstrates that incorporating ultrasonographic measurements into a machine learning model, in addition to clinical airway assessments, improves predictive accuracy. Integrating our predictive model into a mobile app could provide a rapid and objective tool for preoperative airway assessment to identify difficult airways and improve patient safety in anesthesia settings.Trial registrationProspective Observational.

To the Editor: I read with interest the article by Tse et al. [1] concerning the prediction of difficult endotracheal intubation in 471 adult patients presenting for routine elective surgery. Their findings prompt comments on several accounts. First, 62 patients were found to be difficult to intubate [laryngoscopy grade III or IV, Cormack and Lehane classification [2]], which is an incidence of 13%. This is an unusually high incidence of difficult intubation, using the definition described previously, in patients who had no malformations of the airway and no disease of the cervical spine; previous studies have shown this incidence to be around 1% [3-5]. Could this be accounted for by the relative inexperience of the anesthesiology residents performing the endotracheal intubation? Second, the authors found that oropharyngeal Class 3 done according to Mallampati criteria [6] and a thyromental distance <or=to7 cm, when used as predictors of difficult intubation either alone or in combination, had low sensitivity and specificity. These findings confirm those of previous studies [3,5,7] that these predictors are of limited use as clinical tests and contradict the results produced by Frerk [4]. Third, the authors found that use of a head extension angle <or=to80 degrees to predict difficult intubation had a very low sensitivity. Sternomental distance (the distance from the mentum to the upper border of the manubrium sterni with the head fully extended and the mouth closed) has been described by Savva [5] as an alternative method of assessing head extension. When used to predict difficult intubation, a sternomental distance <or=to12.5 cm was shown to have a sensitivity of approximately 80% [5,8]. I agree with the author's comment that designing a good predictive test for difficult intubation is problematic since there are many factors that can cause difficulty. It has been shown that mandibular protrusion Class C as described by Calder et al. [9] is always associated with difficult intubation [8,9]. It has also been shown that there is no correlation between maximum interincisor gap (IG) and difficulty with intubation [5] when the IG is >or=to2.0 cm. It has accordingly been suggested that an IG <2.0 cm should be used to predict difficult intubation. It appears that a sternomental distance <or=to12.5 cm, mandibular protrusion Class C, and IG <2.0 cm should be used as a composite examination having >80% sensitivity in the preoperative screening for difficult intubation. Dino Savva, MB, ChB, DA, FRCA M. Maroof, MD Department of Anesthesiology King Fahd National Guard Hospital Riyadh 11426, Saudi Arabia

To the Editor: I read with interest the article by Tse et al. [1] concerning the prediction of difficult endotracheal intubation in 471 adult patients presenting for routine elective surgery. Their findings prompt comments on several accounts. First, 62 patients were found to be difficult to intubate [laryngoscopy grade III or IV, Cormack and Lehane classification [2]], which is an incidence of 13%. This is an unusually high incidence of difficult intubation, using the definition described previously, in patients who had no malformations of the airway and no disease of the cervical spine; previous studies have shown this incidence to be around 1% [3-5]. Could this be accounted for by the relative inexperience of the anesthesiology residents performing the endotracheal intubation? Second, the authors found that oropharyngeal Class 3 done according to Mallampati criteria [6] and a thyromental distance <or=to7 cm, when used as predictors of difficult intubation either alone or in combination, had low sensitivity and specificity. These findings confirm those of previous studies [3,5,7] that these predictors are of limited use as clinical tests and contradict the results produced by Frerk [4]. Third, the authors found that use of a head extension angle <or=to80 degrees to predict difficult intubation had a very low sensitivity. Sternomental distance (the distance from the mentum to the upper border of the manubrium sterni with the head fully extended and the mouth closed) has been described by Savva [5] as an alternative method of assessing head extension. When used to predict difficult intubation, a sternomental distance <or=to12.5 cm was shown to have a sensitivity of approximately 80% [5,8]. I agree with the author's comment that designing a good predictive test for difficult intubation is problematic since there are many factors that can cause difficulty. It has been shown that mandibular protrusion Class C as described by Calder et al. [9] is always associated with difficult intubation [8,9]. It has also been shown that there is no correlation between maximum interincisor gap (IG) and difficulty with intubation [5] when the IG is >or=to2.0 cm. It has accordingly been suggested that an IG <2.0 cm should be used to predict difficult intubation. It appears that a sternomental distance <or=to12.5 cm, mandibular protrusion Class C, and IG <2.0 cm should be used as a composite examination having >80% sensitivity in the preoperative screening for difficult intubation. Dino Savva, MB, ChB, DA, FRCA M. Maroof, MD Department of Anesthesiology King Fahd National Guard Hospital Riyadh 11426, Saudi Arabia

Bedside screening tests for predicting difficult intubation play a crucial role in clinical practice, although their utility remains limited. This prospective observational study aimed to assess the predictive value of the Acromio-Axillo-Suprasternal Notch Index (AASI) for difficult visualization of the larynx (DVL). Following approval from the Institutional Ethics Sub-Committee (Research Protocol No.: IESC/FP/68/2023), this prospective, observational, single-center study involved a sample size of 100 consecutive adult patients, both male and female, aged 20 to 65 years. The participants were classified as American Society of Anesthesiologists (ASA) grade I or II and were scheduled for elective surgeries necessitating endotracheal intubation.Before the operation, the following factors were assessed: AASI, modified Mallampati test (MMT), sternomental distance (SMD), thyromental distance (TMD), and inter-incisor distance (IID). Larynx visualization was evaluated using the Cormack-Lehane (CL) grading system, where grades III and IV indicate difficult laryngeal visualization. Qualified anesthesiologists performed direct laryngoscopy while remaining unaware of the outcomes of the airway predictors being assessed. The main aim of the investigation was to assess the efficacy of the AASI as a means of predicting DVL. The research study's secondary goals involved evaluating the accuracy of AASI in predicting challenging airways compared to other predictors such as MMT, SMD, TMD, and IID. DVL was observed in 21% of patients, out of which 10 and 11 were males and females, respectively. The sensitivity, specificity, and area under the curve (AUC) of the AASI were observed and reported with a 95% confidence interval (CI), being 98.73% (93.2-99.9%), 71.43% (47.8-88.7%), and 0.851 (0.732-0.970), respectively. AUC analysis revealed that AASI outperformed MMT, SMD, TMD, and IID as a predictor of DVL. AASI (≥0.5) serves as an excellent predictor for DVL during direct laryngoscopy. This finding suggests the clinical utility of AASI in identifying patients who may require special consideration during intubation procedures.

Background/Objectives: Prediction of a difficult airway during pre-anesthetic evaluation is of great importance because it enables an adequate anesthetic approach and airway management. As there is a scarcity of prospective studies evaluating the role of anthropometric measures of the face and neck in predicting difficult airways in infants with an apparently normal airway, we aimed to identify the aforementioned predictors of difficult facemask ventilation and intubation in infants. Methods: A prospective, observational study that included 97 infants requiring general endotracheal anesthesia was conducted. Anthropometric and specific facial measurements were obtained before ventilation and intubation. Results: The incidence of difficult facemask ventilation was 15.5% and 38.1% for difficult intubation. SMD (sternomental distance), TMA (tragus-to-mouth angle distance), NL (neck length) and mouth opening were significantly lower in the difficult facemask ventilation group. HMDn (hyomental distance in neutral head position), HMDe (hyomental distance in neck extension), TMD (thyromental distance), SMD, mandibular development and mouth opening were significantly different in the intubation difficulty group compared to the non-difficult group. HMDn and HMDe showed significantly greater specificities for difficult intubation (83.8% and 76.7%, respectively), while higher sensitivities were observed in TMD, SMD and RHSMD (ratio of height to SMD) (89.2%, 75.7%, and 70.3%, respectively). Regarding difficult facemask ventilation, TMA showed greater sensitivity (86.7%) and SMD showed greater specificity (80%) compared to other anthropometric parameters. In a multivariate model, BMI (body mass index), COPUR (Colorado Pediatric Airway Score), BOV (best oropharyngeal view) and TMA were found to be independent predictors of difficult intubation, while BMI, ASA (The American Society Physical Status Classification System), CL (Cormack-Lehane Score), TMA and SMD predicted difficult facemask ventilation. Conclusions: Preoperative airway assessment is of great importance for ventilation and intubation. Patient's overall condition and facial measurements can be used as predictors of difficult intubation and ventilation.

BACKGROUND: Unanticipated difficult tracheal intubation is a significant source of morbidity and mortality in anaesthetic practice which can be reduced by identification of potential difficult intubation. OBJECTIVE: We aimed the present study to know the incidence of difficult intubation, factors associated with it and the predictive value of various airway predictors in anticipating difficult visualization of larynx and difficult intubation. METHODS: 435 adult patients (>18 year) undergoing general anaesthesia with intubation were examined preoperatively for demographic details (age, sex, weight), dentition, airway pathology and six airway predictors i.e. Inter Incisor Gap (IIG), Modified Mallampatti Grading (MMPG), Upper lip bite test (ULBT), Thyromental distance (TMD), Sternomental distance (SMD) and subluxation of mandible (SLM). All patients were anaesthetized using standard protocol with thiopentone (5mg/kg) and succinylcholine (1.5 mg/kg). On direct laryngoscopy, Cormack Lehane (CL) grading was noted. CL grade I, II was defined as easy visualization of larynx (EVL) and CL grade III, IV as difficult visualization of larynx (DVL). Difficult intubation score (DIS) was calculated as sum of CL grade and number of intubation attempts. DIS of less than or equal to 4 was defined as easy intubation (EI) and DIS > 4 was defined as difficult intubation (DI).Sensitivity, specificity, positive and negative predictive value, positive and negative likelihood ratios(LR) and odd's ratio value for six airway predictor tests was calculated by standard formulae. RESULTS: Incidence of DVL was 12.65% (n=55) and DI was 9.65% (n=42), with no failed intubation. All airway tests had very high negative predictive value (>90%) which implicates they identify easy intubations more precisely. MMPG and ULBT were found as airway predictors for difficult intubation having odds ratio of 85.23 (95% CI 25.42- 285.89%) and 65.45 (95% CI 25.69-166.7%) respectively, along with very high sensitivity of 92.80% and 85.7% respectively. Presence of ULBT III is the best predictor of difficult intubation (+LR 21.97) and absence of MMPG III, IV is the best predictor of difficult intubation (-LR 0.091). Abnormal dentition and airway pathology also increase the risk of difficult intubation, P<0.001. CONCLUSION: We conclude that ULBT and MMPG are nearly perfect airway predictors and should be used routinely during pre-anesthetic visit for screening of difficult intubation.

Background &amp; objective: Difficult intubation remains a risk for patients undergoing general anesthesia (GA) or mechanical ventilation in an intensive care unit (ICU). Macroglossia is a known factor for difficult intubation. But it is not routine to assess the tongue size to predict difficult intubation. Studies are found deficient in comparing usefulness of measuring thyromental distance and the tongue thickness (TT) measured by ultrasonography to estimate difficult intubation. We compared tongue thickness measured by ultrasonography and thyromental distance as a means to anticipate difficult intubation. Methodology: A convenient sample of 60 patients; 32 males and 28 females, who were undergoing elective surgery with GA were included. Thyro-mental distance (TMD), along with tongue thickness (TT) were measured consecutively in each patient in a transitional room. After induction of GA, Cormack Lehane (CL) score was assessed for all patients to detect difficult intubation. Results: Thyro-mental distance was significantly reduced in patients with difficult intubation, while the reverse was in the measurement of tongue thickness; where patients with difficult intubation had significantly a greater TT than those with no difficult intubation. TT measurement had significantly higher sensitivity and specificity (38%, and 96% respectively; P = 0.002) than thyro-mental distance in the detection of difficult intubation. Conclusion: In this study we demonstrated that there was statistically significant inverse relationship of thyro-mental distance on CL, and statistically significant direct relationship of tongue thickness on CL. The results showed that tongue thickness was more effective to detect difficult intubation. Abbreviations: CL - Cormack Lehane; TMD - Thyro-mental distance; TT - Tongue thickness; Keywords: Tongue Thickness; Thyromental Distance; Difficult Intubation Citation: Kadhim AB, Hamid GR. A comparative study between tongue thickness measured by ultrasonography and thyromental distance in anticipation of difficult intubation. Anaesth. pain intensive care 2024;28(3):431−435; DOI: 10.35975/apic.v28i3.2465 Received: March 16, 2024; Reviewed: March 29, 2024; Accepted: March 31, 2024

Obesity is one of the challenging elements in health care. Studies have shown that as the body mass index (BMI) increases, the risk of chronic conditions tends to increase due to altered physiologic and metabolic demands. In addition to underlying physiological changes, anatomical changes can lead to common procedural challenges, such as difficult intravenous (IV) cannulation, difficult airway, and difficult intubation, which makes their preoperative and postoperative care challenging for the anesthesiologists. According to previous studies, there is no single best predictor for difficult airway or intubations and no designed protocol for choosing an intubation technique in obese patients. Some of the preoperative risk factors and techniques such as the modified Mallampati class, sternomental distance, thyromental distance, neck circumference, indirect mirror laryngoscopy, BMI, and intraoperative risk factors such as inappropriate positioning of the patient, suboptimal medication dosing, inappropriate laryngoscopy device acted as independent predictors for difficult airway and difficult intubation. Analyzing each element’s importance and making suitable decisions for the individual will reduce the complications and prepare for unplanned emergencies in the operating room. This review is convincing with previous studies that obesity itself is not an independent predictor. Instead, as a preoperative risk factor, and till date, sternomental distance and the number of intubation attempts were demonstrated as significant independent predictors for adverse events. All the other independent factors and considerations were discussed, which can help with further research.